There are two broad categories of garage doors in common use which include one-piece canopy doors and track guided multisectioned doors. The latter category of doors has interconnected sections which are supported at both ends in tracks which extend along the sides of the door opening and continue along the ceiling of the garage so that the connected sections may be slid upwardly and inwardly from a closed to an open position. The one-piece canopy door is typically used for smaller garage openings and is less costly than the many hinged sections used in the multisection doors. In addition, the rollers and tracks used in multisection doors add installation costs and complications not associated with the canopy doors.
There are a number of different types of mechanisms used to support and move the canopy type door between its open and closed positions. The mechanism supports the door for pivotal movement between a vertical and horizontal position and at the same time raises it to the level of the top of the door opening as it moves to the horizontal position. Because of the space limitations arising from the garage ceiling being only slightly higher than the top of the door opening, the door opening mechanism must occupy a very limited vertically extending space above the door opening. As a consequence, the mechanism cannot project any appreciable distance above the door in its open, horizontal position. It is also important that the mechanism not swing the door horizontally inwardly any appreciable amount since such movement would subtract from the usable space within the garage.
One of the more commonly used mechanisms for supporting a canopy garage door is a type of slide crank mechanism wherein the door constitutes a connecting rod extending between the free end of a crank arm pivoted at the top of the door opening and a sliding bearing received in a vertical track along the edge of the door opening. Thus, there are two crank arms which pivot at the opposite edges of the door so that the crank arms move through an angle of approximately 90.degree. as the door moves from the vertical to the horizontal open position with the crank arms essentially in line with the door in either the open or the closed door position. The above described door opening mechanism is shown in the European Patent No. EP 0029423, which issued Apr. 18, 1984. Examples of other types of mechanisms for supporting canopy type garage doors are shown in Snyder U.S. Pat. No. 2,912,237, Marmont et al. U.S. Pat. No. 2,985,446 and Hahn U.S. Pat. No. 2,753,179.
Many of the currently used mechanisms for supporting canopy type garage doors are relatively simple to operate manually. The doors are normally provided with springs to counterbalance the weight of the door. As a result, it is relatively easy for a person to open or close these doors by applying a lateral force and a vertical force in the form of a lifting force or a pull downwardly to overcome the inertia of the door and move it from one position to the other. However, it is often desired to equip such canopy doors with an automatic opening mechanism. In an automatic opening mechanism for a sectional door, it is relatively simple to secure the mechanism to the top of the door and draw the top edge of the door in almost a straight line along the horizontal portion of the door guiding track. The problem of equipping a canopy door with an automatic opener is much more complicated as a consequence of the combined rotational and translational movement of the canopy door in moving between the opened and closed positions.
The typical automatic garage door opening mechanism includes a carriage which is motor driven along a track or T-bar by means of a screw or a roller chain with the carriage moving back and forth along a rectilinear path. A coupling means is provided to interconnect the carriage to the door, with there normally being a disconnect means to decouple the carriage from the drive to permit manual operation of the door in the event of a malfunction or a power failure. While it is possible to design an automatic door opening mechanism specifically for the particular motion associated with a canopy door, it is preferable from a manufacturing cost standpoint and an inventory cost standpoint to use the same door opening mechanism for as many different types of doors as possible. It is also noted that most of the automatic garage door openers sold are for the multisectioned doors rather than the canopy doors. Accordingly, it would be desirable to adapt to use on the canopy door the typical automatic opening mechanism having a carriage which moves on a rectilinear path along a track. The Snyder and Marmont et al. patents cited above are examples of powered door opening mechanisms which are designed specifically for canopy door applications.
In order to understand the difficulty in driving a canopy door using the slider crank mechanism shown in the above cited European Patent with a rectilinear carriage movement, it is helpful to consider the forces necessary to initiate movement of the door from either the open or closed position. On the movement from the closed position, the door, the crank arms and the door bearings are all in line on a vertical line. If the carriage moves horizontally from a position above the door, it must pivot and lift the door at the same time and this action must be initiated from a position in which it applies enough forward pressure to hold the door closed. The three lever mechanism of the European patent cited above purports to perform this function of initiating movement from the closed position.
As the door moves toward the horizontal, open position, the door opening mechanism must provide sufficient rotating force on the door to lift the bottom edge of the door against the force of gravity toward the top of the door opening. In this position the door is substantially parallel to the path of movement of the carriage of the opening mechanism, making it difficult for the carriage movement to bring the door to the full open position. As soon as the process is reversed, the carriage moves in the door closing direction when it must provide a turning moment in the reverse direction to move the bottom of the door downwardly. The closing movement of the carriage tends to be along the line of the crank arms, which would restrain movement of the carriage until the door begins to rotate.
There are essentially two problems involved in the initial movement of the door from its open position toward the closed position. One relates to the in-line position of the bearings and need for a turning moment to start the door moving. The second problem relates to the slow movement of the top edge of the door in the horizontal direction as it begins its turning movement. More accurately, it should be described as the small amount of horizontal movement of the door for a certain amount of rotary movement. As the closing proceeds, much more horizontal movement is required to produce the same amount of rotary movement. Since the driving carriage of the door closer moves horizontally at a constant velocity, the carriage must move the door through a greater rotary movement initially than later in the closing cycle. As a consequence, the load on the motor tends to be very high in the initial portion of the closing cycle.
Further, as the canopy door moves into the closed position, the carriage must apply sufficient lateral force against the door to prevent it from being blown open or forced open. This force direction is difficult to achieve with the carriage position being above and adjacent to the door.
Another serious consideration in the design of a canopy automatic door opening mechanism relates to the necessary overload reverse switches. It is conventional to provide automatic garage door opening mechanisms with reversing means in the motor circuit so that if the door, on moving in the closing direction, encounters an obstruction, the door opening mechanism will reverse and open the door. This response is typically tied to an adjustable level of overload motor current or to a decrease in the rotating speed of the motor. Thus, as the motor draws more current or slows in speed upon encountering an obstruction, the circuit automatically reverses the direction of motor rotation to raise the door. The related problem involved with canopy doors is that fact that load on the motor is extremely variable in the automatic opening mechanism for a canopy door. As discussed above, at the initial stage of closing the door, the force required to be exerted by the carriage increases substantially. If the automatic opening mechanism is designed to perform continuously under the load conditions encountered near the open and closed positions, the overload reversal switching will, of necessity, occur at a high level of motor current or at a slow speed. Under such circumstances, there is risk of property damage, or damage to the door itself before the motor reversal would take place. Accordingly, it is desirable to reduce the peak power requirements during the opening and closing cycles to allow the reverse to be set at as low a current level or high a speed level as possible. Thus, it would be preferable to even out the load demand on the motor so that the reversal could be caused with only a small increase in motor current or a small decrease in motor speed.
Another problem associated with the canopy door is related to the nature of the door movement at closing as well as the manner in which it is driven. Only about one-third of the length of the door extends below the sliding bearing that engages the vertical track. As the door moves to its closed position, the top of the door is driven a greater distance than the bottom of the door which moves a relatively short distance. This provides a mechanical advantage by which a relatively small force at the carriage produces a large force at the bottom of the door. Again, if the overload reversal cannot be set at a relatively low value, the bottom of the door can apply a large force before reversal occurs. Accordingly, it is important to maintain the overload reversal level as low as possible by providing a drive mechanism which reduces the power peaks and evens out the load on the motor throughout the opening and closing cycles.
In addition to the one-piece canopy doors discussed above, there are other types of garage doors which present similar problems to those discussed above in connection with the canopy doors in adapting them to use with door openers having the rectilinear motion drive means. These other types include dual track, one-piece doors and bifold doors. The dual track doors have vertical and horizontal tracks extending up the sides of the door opening and inwardly from the top of the door opening to slidably support bearings on the sides of the door. Both of these types of doors require rotational and translational forces for opening and closing. Accordingly, the use of automatic door openers having reciprocating drive means that move horizontally on a rectilinear path with the dual track and bifold doors have presented the same types of problems as were discussed above in connection with the canopy door.